A bass is a type of classical male singing voice and has the lowest vocal range of all voice types. According to The New Grove Dictionary of Opera, a bass is typically classified as having a vocal range extending from around the second E below middle C to the E above middle C (i.e., E2–E4). Its tessitura, or comfortable range, is normally defined by the outermost lines of the bass clef. Categories of bass voices vary according to national style and classification system.